Process for oil recovery using multifunctional anionic surfactants

ABSTRACT

A process for the recovery of oil from subterranean reservoirs by injecting an aqueous fluid containing from about 0.05 to about 2.0% by weight of a surfactant of structure 
     
       
         
         
             
             
         
       
     
     where m+n=1-30 or more,
 
x+y=0-28,
 
EO=oxirane,
 
PO=methyl oxirane,
 
M=H, Na, K, NH 3 , Amine, Ca, Mg,
 
R and R1 are each separately and independently H, branched or linear alkyl, branched or linear alkenyl,
 
A=aromatic, and,
 
a+b=0 to 30.

CROSS REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

DESCRIPTION OF ATTACHED APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to a process for the recovery of oil from subterranean oil bearing reservoirs, and more particularly the present invention is to improved oil recovery involving the injection into reservoirs of a composition containing anionic surfactants having both ether carboxylate and sulfonate groups on the same molecule.

In the recovery of oil from subterranean reservoirs It usually Is possible to recover approximately 15%-20% of the original oil in place by primary recovery. Secondary recovery methods such as well stimulation or water flooding are applied after the amount of oil recovered by primary recovery becomes uneconomical. Secondary recovery methods can recover approximately an additional 15%-30% of the original oil in place which leaves the reminder of the oil unrecoverable unless other means such as tertiary recovery processes are applied. These tertiary recovery methods include but are not limited to the use of miscible and immiscible gases and liquids, steam, foam, alkali, surfactants, and polymers.

It has been known that many factors including but not limited to the interfacial tension (IFT) between the injection brine and the residual oil, the relative mobility of the injected brine, and the wettability characteristics of the rock surfaces comprising the reservoir are all important in determining the amount of oil recovered by tertiary recovery. Numerous studies have found that the addition of surfactants to the injection brine can after the interfacial and wetting properties to help overcome the high capillary pressure and increase the oil recovery. In many cases the addition of a polymer along with the surfactant or immediately after the surfactant can increase the mobility ratio between the injected brine and oil thus further improving the sweep efficiency of the flood.

Because the injection brine composition varies, it is important to use the brine available at the injection site for the oil recovery process in order to be economically feasible. It is important to have surfactants that are compatible with brines having wide ranges of total dissolved solids (TDS) and divalent cations such as those of calcium and magnesium. The problem with many of the presently used surfactants in tertiary oil recovery is that they are incompatible with the brines containing high TDS and divalent cations that are often found at the injection site. Costly water treatment processes or using an alternate fresh water source makes the oil recovery process economically unfeasible in many cases. Therefore it is important to have surfactants that are tolerant to the high TDS and divalent cations. It is also important that the surfactant be tolerant to the high temperatures encountered in some wells and has lower adsorption on to the reservoir rock. Most surfactants cannot meet all these requirements and in many cases blends of several different types of surfactants are used to meet the specific requirements. When blends are used a strong possibility of chromatographic separation exist as the surfactant blend propagates through the reservoir due to differential adsorption properties losing it's effectiveness in IFT reduction or wettability alteration.

Anionic sulfonate surfactants are often used in the oil recovery process to reduce the IFT and higher temperatures because of their thermal stability. However sulfonates are not tolerant to brines of high salinities and high divalent cations. Ether carboxylates are tolerant to high temperatures, high salinities and high divalent cations but they often fail to give the required low IFT required to recover oil. The present invention involves the use of surfactants having to provide the functions suitable for oil recovery without the disadvantages of using single components or the mixture of one or more components. Many examples of using mixtures of two or more surfactants to lower interfacial tension and recover residual oil can be found in the literature. U.S. Pat. No. 8,022,834 issued to Hsu et al discloses the use of mixtures of carboxylated anionic surfactants with sulfonated surfactants. U.S. Pat. No. 4,458,759 issued to Isaacs teaches a composition comprising organic sultanate surfactants such as sulfonate fatty acids having both weak and strong anionic functionality groups. These products are derived from fatty acids and as such can form esters but cannot form stable ethers when reacted with ethylene or propylene oxides and therefore do not exhibit the thermal stability of the compounds described in the present invention. Processes and surfactants have been described in the literature using sulfonated oleic acid, for example, U.S. Pat. No. 3,575,883 to Foley. Besides being derived from acids to give unstable esters when alkoxylated, these employ conventional means of sulfonation and are limited to lower molecular weight products because of reduced sulfonation efficiency with high molecular weight products. The products of the present invention use a different sulfonation procedure and are not limited to low molecular weight products. Therefore highly alkoxylated products of molecular weights exceeding 1000 can be easily manufactured. The composition of the present invention is an ether carboxylate having an additional sulfonate group on the molecule. The ether carboxylate group has been shown to be very salt tolerant and thermally stable. The sulfonate group provides thermal stability as well as lowering the interfacial tension. The two negative charges on the same molecule help to lower adsorption unto reservoir rock that is usually negatively charged by electrostatic repulsion. This combination of an alkyl ether carboxylate and an alkyl sulfonate attached to an aromatic spacer disclosed in the present invention is unique and provides synergistic performance that has not been anticipated before.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

An objective of the present invention is to provide a process for the recovery of oil from subterranean reservoirs using a surfactant composition to improved oil recovery that is effective over a wide range of temperatures, electrolyte and divalent anion concentrations, and is not subject to chromatographic separation.

Another objective of the present invention is to provide a process for the recovery of oil from subterranean reservoirs using a surfactant composition to improved oil recovery with minimum adsorption onto the formation.

Other objectives and advantages of the present invention will become apparent from the following descriptions, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.

The present invention is directed to the composition containing surfactants having an ether carboxylate functional group and a sulfonate functional group on the same molecule, which composition is formulated into a concentrated surfactant blend containing an aqueous solvent such as water or brine, and optionally a co-surfactant/solvent such as a lower molecular weight alcohol or alcohol ether. The concentrated surfactant blend is added in a concentration range of about 0.05% to about 5% to the injection brine and introduced into the subterranean hydrocarbon containing formation by (a) injecting into said formation through one or more injection wells, and (b) displacing said solution into the formation to recover hydrocarbons from one or more production wells. The injection and producing wells may be the same or different. Depending on the reservoir conditions, other additives may be added to the injection brine including strong or weak alkalis, viscosifiers, corrosion and scale inhibitors, and others known to those familiar with the art.

In the present invention, the ether carboxylate group and the sulfonate groups on the same molecule provide several advantages over mixtures of surfactants having each of the functionalities on separate molecules. The single molecule containing the two groups eliminates the possibility of chromatic separation when subjected to a strong adsorbent such as when injected into an oilfield reservoir.

Structure I below describes the compound of this invention. This structure shows the aromatic group to be a single ring structure. Multiple ring structures including but not limited to naphthalenes or phenyl ethers are also part of the present invention.

Where,

A=aromatic R and R1 are each separately and independently H, branched or linear alkyl, branched or linear alkenyl, m+n=1-30 or more, x+y=0-28, EO=oxirane, PO=methyl oxirane,

M=H, Na, K, NH₃, Amine, Ca, Mg,

a+b=0 to 30.

The product described in Structure I is made by reacting an unsaturated ether carboxylate with sulfonio acid Structure II. The procedure for obtaining Structure I is described in U.S. Pat. No. 6,043,391. The addition of ethylene oxide and/or propylene oxide to an alcohol, followed by carboxylation to form alcohol ether carboxylates gives these carboxylates salt and divalent cation tolerance and thermal stability.

Where

A=aromatic, including but is not restricted to benzene, toluene, xylene, naphthalene, diphenyl ether, R, R₁ are each separate and independently H, branched or linear alkyl, branched or linear alkenyl,

R₂═H,

a+b=0 to 30.

The unsaturated carboxylate moiety may contain from about 0 to about 30 or more moles of an alkoxy group such as ethylene oxide (EO), propylene oxide (PO), or mixtures of EO and PO, or sequences of EO and PO, to adjust the solubility and molecular weight of the surfactant. Unsaturated ether carboxylates include but are not limited to oleyl alcohol ether carboxylates, erucyl alcohol ether carboxylates, nervonyl alcohol ether carboxylates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.

The present invention is directed to a high salinity, high divalent cation and high temperature tolerant, low adsorption surfactant.

The present invention also includes a process using compositions containing surfactants described in Structure I to recover oil from subterranean reservoirs. For this process Structure I is usually formulated into a concentrated surfactant blend at levels of 5 to 80 wt % or more in an aqueous solvent such as water or brine, and optionally a co-surfactant/solvent such as a lower molecular weight alcohol, or alcohol ether, and optionally a pH control agent. Non-exclusive examples of the co-surfactant/solvent are iso-propanol, n-butanol, and ethylene glycol monobutyl ether. The concentrated surfactant solution is added in a concentration range of about 0.05% to about 5% to an injection fluid or brine and introduced into the subterranean hydrocarbon containing formation by (a) injecting into said formation through one or more injection wells, and (b) displacing said solution into the formation to recover hydrocarbons from one or more production wells. The injection and producing wells may be the same or different. Depending on the reservoir conditions, other additives may be added to the injection brine including strong or weak alkalis, viscosifiers, corrosion and scale inhibitors, and others known to those familiar with the art. Gases including but not limited to N₂ or CO₂ can also be used to inject the surfactant into the reservoir.

The concentrated surfactant blends containing structure I have been found to be compatible with a wide range of brines containing different amount of total dissolved solids and multivalent cations such as Ca⁺² and Mg⁺² and very stable to high temperatures exceeding 150° C.

In accordance with a preferred embodiment of the invention, there is disclosed a process for improving the recovery of oil by injecting into one or more injection wells a fluid containing

a) one or more surfactants described in structure I,

b) an aqueous solvent,

c) optionally one or more co-surfactants/solvents,

d) optionally a viscosity increasing agent, and

e) optionally an alkali,

and, recovering the oil from one or more of the same or different producing wells.

The aqueous solvent may be water or a synthetic brine or a brine that is produced from the reservoir. The co-surfactant/solvent includes, but is not limited to, a short chained alcohol, glycol, or ether such as methanol, ethanol, propanol, isopropanol, butanol, iso-butanol, glycerin, ethylene glycol, propylene glycol, ethylene glycol monobutyl ether. The alkali includes but is not limited to sodium hydroxide or sodium carbonate, organic alkali. Organic alkalis include, but are not limited to, salts of weka acids and salts of polymerized weak acids. The viscosity improving agent includes, but is not limited to, any of a number of polymers known to those familiar with the art including polyacrylamide, xanthan gum, and block polymers of acrylamide and copolymer of acrylic acid and 2-Acrylamido-2-Methylpropyl Sulfonic Acid (AMPS).

Following are examples illustrating the utility of the present invention for application in the recovery of oil from subterranean reservoirs. The interfacial tension (IFT) between the crude oil/injection brine using the composition of the present invention is used to illustrate the efficiency of the present invention. It is well documented that after primary oil recovery and secondary oil recovery the Capillary Number is about 10⁻⁸ [See for Instance Basic Concepts In Enhanced Oil Recover Processes, p 18-19, 90]. The capillary number is defined as:

Nc=μV/σ

where

Nc=Capillary Number

μ=displacing fluid viscosity V=interstitial velocity σ=IFT between the displacing fluid and the crude oil.

Increasing the Capillary Number to a value above 10⁻³ has been shown to result in a substantial increase in the recovery of trapped oil after waterflooding has become ineffective (Basic Concepts in Enhanced Oil Recover Processes, p 108). The viscosity and the velocity cannot be increased substantially without damaging the reservoir; however, the IFT can easily be reduced 3 to 4 orders of magnitude by the proper choice of surfactant. Thus a surfactant can reduce the IFT between an oil and an aqueous medium from 3-30 mN/m to less than 10⁻² mN/m resulting in an increase in the capillary number to greater than 10⁻² and improve the oil recovery.

In the following examples, IFT has been used as a measure of the suitability of a particular surfactant as a candidate for enhanced oil recovery.

Table I lists the surfactants used to in the examples chosen to demonstrate the utility and novelty of the invention. In all cases the surfactant formulation consisted of 30% by weight surfactant, 25% by weight ethylene glycol monobutyl ether (co-surfactant/solvent), and 45% by weight water. Also in all cases the surfactant formulation was added to the injection brine at a concentration of 0.10 weight percent. These examples use surfactants containing only ethylene oxide in the alcohol ether carboxylate although products containing propylene oxide and ethylene oxide give good results in certain applications.

TABLE I Surfactants Used In Examples SURFACTANT CHEMICAL DESCRIPTION A Structure I where x = 7, y = 8, m = 0, n = 2, M = Na, and a + b = 11. B Structure I where x = 7, y = 8, m = 0, n = 9, M = Na, and a + b = 11. C Sodium salt of carboxylated oleyl alcohol with 2 moles of EO. D Sodium salt of carboxylated oleyl alcohol with 9 moles of EO. E Sodium salt of structure II where a + b = 11

Table II is the brine compositions that were used for the IFT testing to show the effect of total dissolved solids and divalent ion concentration on the IFT obtained using various surfactants.

TABLE II Brine Compositions BRINE 1 2 3 4 5 NaCl, % 3.0 1.0 5.0 10 20 CaCl2—2H2O, % 1.0 0 0 0 0 MgCl2—6H2O, % 1.0 0 0 0 0

Table III compares the solubilities obtained with 5.0% by weight of various surfactant concentrates in the 5 brines at 30° C.

TABLE III Brine Solubilities SURFAC- BRINE BRINE TEST TANT BRINE 1 2 3 BRINE 4 BRINE 5 1 A soluble soluble soluble insoluble insoluble 2 B soluble soluble soluble soluble dispersible 3 C dispersible soluble soluble soluble dispersible 4 D soluble soluble soluble soluble soluble 5 E insoluble soluble in- insoluble insoluble soluble 6 C + E insoluble soluble in- insoluble insoluble soluble 7 D + E insoluble soluble in- insoluble insoluble soluble

Table III shows the unexpected result that the various surfactants where the sulfonate and ether carboxylate are on the same molecule are soluble in all the brines tested whereas in many cases the individual sultanates (E) and mixtures of the sulfonates and alcohol ether Carboxylates (C+E and D+E) are not.

Tables IV and V shows the interfacial tension (IFT) in millineutons/meter (mN/m) against a crude oil having 27 API Gravity at 95° C. for 0.1 wt % surfactant. All IFTs were obtained using a University of Texas Model 500 spinning drop interfacial tensiometer after spinning at 95° C. for 1 hour. The data shows low IFT can be obtained with low surfactant concentration when the amount of ethylene oxide averages 3.8 to 8.8 Moles/Mole of oleyl alcohol.

TABLE IV IFT Properties SURFAC- BRINE BRINE TEST TANT BRINE 1 2 3 BRINE 4 BRINE 5 1 A 0.891 0.005 0.012 insoluble insoluble 2 B 0.356 0.009 0.003 0.003 0.002 3 C 0.769 0.070 0.090 0.122 0.256 4 D 0.066 0.031 0.022 0.020 0.020 5 E insoluble 0.007 in- insoluble insoluble soluble 6 C + E insoluble 0.005 in- insoluble insoluble soluble 7 D + E insoluble 0.009 in- insoluble insoluble soluble Table V also shows that the individual surfactants A and B containing 2 and 9 moles of ethylene oxide respectively do not give ultra-low IFTs with brine 1; however blends containing various amounts of the two do give IFTs below 10⁻² mN/m.

TABLE V Comparison of IFTs with Various Surfactant Mixtures Avg Mole A wt % B wt % EO BRINE 1 100 0 2.0 0.891 75 25 3.8 0.0080 50 50 5.5 0.0058 25 75 6.8 0.0023 0 100 9.0 0.356

Table VI shows the IFTs obtained using individual surfactants defined by structure I where the moles of EO are have been varied from 2 to 9. This shows that the single surfactant system can give the same IFT values as the blends from Table IV with the additional advantage of having no possibility of chromatographic separation since they are single component systems.

TABLE VI IFT for Various Single Component Systems Mole EO BRINE 1 2.0 0.891 4.0 0.0080 6.0 0.0051 7.0 0.0035 8.0 0.093 9.0 0.356 Table VII compares the adsorption of the composition of this invention surfactant B with a 1:1 molar mixture of surfactant D and surfactant E to show the effectiveness of having both the sulfonate and ether carboxylate on one molecule. 0.2 wt % surfactant D and 0.2 wt % surfactant E alone were also included to correct for the amount of each of these surfactants adsorbed. All tests were done using 0.20 wt % total surfactant in Brine 2. The static adsorption was run by mixing 50.0 grams of surfactant solution with 10.0 grams of 200 mesh beach sand on a wrist action shaker for 16 hours and than determining the amount of surfactant remaining compared to the original amount added. Table VII shows the amount adsorbed in mg surfactant/gram sand.

TABLE VII Adsorption Tests Original Amount wt, g remaining Adsorbed mg/g % adsorbed Surfactant B 0.100 0.096 0.014 1.4 14 Surfactant D + E 0.100 0.039 0.061 6.1 61 Surfactant D 0.100 0.022 0.078 7.8 78 Surfactant E 0.100 0.045 0.055 5.6 55 The data from Table VII shows that the alcohol ether carboxylate (surfactant D) is strongly adsorbed (78%) onto the send. The sulfonate (surfactant E) is not adsorbed as much however this product is not compatible with brines having salt concentrations of 5 wt % or more as shown in Table III. The mixing of surfactant E and surfactant D indicates that the adsorption of surfactant D is very large and not reduced by mixing with surfactant E, However, the adsorption of the composition of this invention surfactant B is very low. This indicates that an unexpected synergistic effect occurs when the alcohol ether carboxylate and the sulfonate are combined on the same molecule.

While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 

1. A process for the recovery of oil from subterranean reservoirs where a surfactant composition is injected into one or more injection wells and the oil recovered from one or more producing wells where said surfactant composition is comprised of a) one or more surfactants having both a sulfonate and an ether carboxylate functionality group on the same aromatic molecule with the structure

Where, A=aromatic, R and R1 are each separately and independently H, branched or linear alkyl, branched or linear alkenyl, EO=oxirane, PO=methyl oxirane, m+n=1-30 or more, x+y=0-28, a+b=0 to 30, and M=H, Na, K, NH₃, Amine, Ca, Mg, b) an aqueous solvent, e) and, recovering the oil from one or more of the same or different producing wells.
 2. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the one or more surfactants having both a sulfonate and an ether carboxylate functionality group on the same molecule are derived from an aromatic molecule.
 3. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the aromatic is selected from the group consisting of benzene, toluene, xylene, naphthalene, phenyl ether.
 4. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the one or more surfactants is present at a concentration from about 0.05 to about 2% by weight of the total injected aqueous solvent.
 5. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the co-solvent is selected from the group consisting of short chain alcohol, glycol, glycerin, glycol ether.
 6. (canceled)
 7. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the aqueous solvent is selected from the group consisting of water, synthetic brine, injection brine, produced brine.
 8. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the one or more injection wells may also serve as the one or more producing wells.
 9. The process for the recovery of oil from subterranean reservoirs described in claim 1 where the one or more injection wells are different than the one or more producing wells. 